Slow it, spread it, soak it.
Extreme flooding events are a part of living in the Wet Tropics, but even here floods are predicted to get worse with climate change. So what can we do to reduce the impacts and damage of floods on our landscapes, waterways and infrastructure?
Ideally our urban areas should include lower-density neighbourhoods with lots of green spaces and trees as well as targeted engineered solutions.
Urban infrastructure in the Wet Tropics has been built on the principle of ‘hard and fast’. Drains and gutters are designed to remove water from the land as quickly as possible to prevent flooding. However, there is growing evidence that this won’t be effective in future with heavier rainfall and rising sea levels, so we need a paradigm shift. Rather than hard and fast, we need to work better with our natural systems and introduce softer infrastructure to help ‘slow it, spread it and soak it’.
A new project by Cairns Regional Council in the Saltwater Creek catchment is working with scientists at James Cook University to model the impacts of flooding under different climate scenarios and to identify and assess potential options for mitigation.
Lynne Powell, Coordinator of Sustainability and Climate Change at Cairns Regional Council, says installing flood mitigation solutions in urban areas involves a lot of risk. The modelling data from this project will help to understand how water behaves in the catchment and will be used when designing solutions.
“Saltwater Creek is a heavily urbanised catchment with a high flood risk,’’ she says. “Before we start planning for how we can mitigate flooding we need good evidence, which also includes Traditional Owner knowledge. One thing we’ve learned is that we need very localised solutions. We need to plan right down to individual sub-catchment level and use a range of different solutions tailored to each area and layered on top of each other. There is no one-size-fits-all solution.”
James Cook University hydrology researcher Dr Han She Lim says the modelling will assess design solutions for households, businesses and schools, as well as for the council. Some potential solutions include green roofs and walls, rainwater tanks, bioretention basins, vegetated drains and landscape planter boxes, all of which are designed to intercept stormwater runoff.
“The designs that we come up with need to be tailored to local catchments and engineered for our climate conditions,’’ she says. “Many of these solutions are already being adopted in other Australian cities but we will need to engineer the designs to suit our tropical climate. For example, to prevent mosquitoes breeding we need to modify designs to hold water only for a maximum of one to two days.
“One of the outcomes of this project will be to develop design guidelines for our region. Hopefully they will be useful for other tropical areas too since Cairns has the potential to be a good model city for others.”
Dr Lisa Law, an urban geography and planning researcher at James Cook University, says there’s a lot more we can do to improve the sustainability of our urban areas, and we need more ‘water-sensitive design solutions’.
“Ideally our urban areas should include lower-density neighbourhoods with lots of green spaces and trees as well as targeted engineered solutions,’’ she says. “While we can do this easily with new developments, retro-fitting older suburbs is much more challenging, so we will need to be innovative.
“Changing from hard and fast to soft infrastructure requires a paradigm shift, particularly because it will involve more maintenance. But the benefits for future liveability, flood mitigation and water quality flowing to the reef make it a no-brainer.”